Satisfied, she declares the bar ready for business. The first customer comes in an orders a beer. They finish their drink, and then ask where the bathroom is.
I just came up with a variation to this off the top of my head.
A QA engineer walks into a bar. She orders a beer. She walks out of the bar. She walks into the bar. She walks into the bar. She walks out of the bar. She walks out of the bar. She walks out of the bar. She orders a beer.
It's very simple: you test things because we can't rely 100% on developers to create the right thing or to create it without any bugs. The same goes for automated test software. I've personally created unit tests that were failing for like 2 years but due to a bug still showed green in CI.
To go back to the joke: manual QA is infinitely more likely to find the exploding bathroom than a unit test would ;)
Automated testing is a fantastic tool, but manual QA is still very valuable.
It's not an either/or though. Used to have an assignment where we as developers would write automated tests (regression tests), while we had an experienced software tester with an excel sheet verifying things by hand. But instead of just following the sheet - which is automatable - he knew of a number of different techniques and approaches and he'd still find a lot of issues that nobody else found. For which we'd write a test to avoid it happening again.
I mean I wouldn't have minded if they wrote more automated tests themselves, but I'm also very aware that the mindset of me and developers would quickly become "it's not my responsibility to test my software".
It's weird how many bugs I regularly find in our software by actually testing things by hand, as opposed to our QA department, which does only automated testing and insists they have covered 100% use-case scenarios.
She orders 2 beers.
She orders 0 beers.
She orders -1 beers.
She orders a lizard.
She orders a NULLPTR.
She tries to leave without paying.
Satisfied, she declares the bar ready for business. The first customer comes in an orders a beer. They finish their drink, and then ask where the bathroom is.
The bar explodes.